EP2910382A1

EP2910382A1 - Platen roller presence detection system for thermal printing device

Info

Publication number: EP2910382A1
Application number: EP14155932.8A
Authority: EP
Inventors: Denis Montagutelli
Original assignee: APS Trading OOD
Current assignee: APS Trading OOD
Priority date: 2014-02-20
Filing date: 2014-02-20
Publication date: 2015-08-26
Also published as: WO2015124412A1

Abstract

The invention relates to the thermal printing device with the so called "easy-loading" system for the paper. Thermal printing mechanism comprising: a printer chassis (2), a thermal printhead (1), platen roller (3) having a conductive shaft (6), the platen roller (3) being designed to be movable between two possible positions - open, where the platen roller (3) is detached from the printer chassis (2) and printing position where the platen roller (3) is held in the printer chassis (2), and motion means (11) to put the platen roller (3) in rotation. It further comprises two lateral conductive contacts (4 and 5) arranged on the printer chassis (2) so as to be in a contact with the two opposite ends of the platen roller conductive shaft (6) in the printing position of the platen roller (3) for conducting electrical current, thus forming an electrical switch for indication of the status of the platen roller position.

Description

TECHNICAL FIELD OF THE INVENTION

The invention relates to the thermal printing device with the so called "easy-loading" system for the paper.

PRIOR ART

Direct thermal printer is a widely used printing technology. A thermal printing mechanism usually comprises a chassis for holding all of the following components: a thermal printhead, a platen roller that can be put in rotation by a motor through a gear train, and pressure means in order to keep under pressure the thermal printhead against the platen roller. A thermal sensitive paper is inserted between the platen roller and the thermal printhead, and the printout is generated by combining the paper advance with the dot selection and activation on the thermal printhead.
An improvement of such device is providing the possibility to separate the platen roller from the thermal printhead and the chassis in order to facilitate the loading of the paper and its positioning between the thermal printhead and the platen roller. In such arrangement the platen roller has two positions: first one called the printing position, where the platen roller is held in the printer chassis and allows the printer to print, and second one - called open position wherein the platen roller is detached by the printer chassis. Such arrangements of a thermal printing mechanism are well known in the prior art, and described for example in FR2786727 .
In addition such devices can comprise also a sensor on the printer chassis to sense the presence of the paper. Such sensor is in most of the cases an optical reflective sensor, and in some specific cases a transmittive sensor or a micro-switch. Such sensor can also be used to detect the separation of the platen roller out of the printer chassis.
This last detection is not very reliable. In particular it is based on the fact that when the platen roller is in the printing position, the combination of its position with the paper guide which guides the paper into the printer mechanism and also holds the optical sensor, forces the paper to make a «S» shape curve. Then, when the platen roller is detached and moved away from the printer chassis, the paper tends to go back in a straight shape, thus increasing its distance from the optical sensor.
Such detection system requires an analog to digital conversion on the electronic board, moreover since the optical sensor has an important gain variation from one to another, a calibration procedure has to be done on the electronic board which measures the electrical signal coming out form the optical sensor, making this detection complex to setup and operate and not always reliable.
Using such sensors increase the overall dimensions and production costs of the thermal printing mechanism that presently have become more and more important requirements for such devices.

SUMMARY OF THE INVENTION

The aim of the present invention is to avoid such optical sensor and realize the function of detecting of the platen roller presence in printing position using usual parts of the thermal printing mechanism. This would allow keeping the overall dimensions of the device in a desired range, simplifying the construction using less components and thus decreasing production costs of the device. The present invention proposes a solution by using the platen roller itself to detect its presence in the printing position in the printer chassis.
The above mentioned aim is achieved by the thermal printing mechanism according to the present invention that comprises:

a printer chassis,
a thermal printhead,
a platen roller having a conductive shaft, the platen roller being designed to be movable between two possible positions - open, where the platen roller is detached from the printer chassis, and printing position, where the platen roller is held in the printer chassis,
motion means to put the platen roller in rotation.

According to the present invention the thermal printing mechanism further comprises two lateral conductive contacts arranged on the printer chassis so as to be in a contact with the two opposite ends of the platen roller conductive shaft in the printing position of the platen roller for conducting electrical current, thus forming an electrical switch for indication of the status of the platen roller position.
The platen roller is usually made of a metallic shaft, so a conductive material, over which a rubber material is molded and rectified to get a precise geometrical cylinder shape which is to be pressed against the thermal printhead. Thus, by rubber being nonconductive, the platen roller shaft is isolated along almost its entire length except for its two opposite free ends. Providing two corresponding contacts on the printer chassis able to contact with the free ends of the platen roller shaft and electrical current allows detecting the presence of the platen roller in the printing position. In such arrangement the platen roller shaft behave as an electrical switch.
When the platen roller is in the printing position, its presence can be detected, since both contacts at each ends of the platen roller are electrically connected trough the platen roller conductive shaft. This position of the platen roller shaft is called the closed switch position, equivalent to the printing position, contrary - the open switch position when no electricity is flowing trough the platen roller conductive shaft, corresponds to the mechanically open position, when the platen roller is detached from the printer chassis.
The switch open or closed positions are perfectly reflected by the electrical connection or disconnection of the two contacts located at, and in contact with each end of the platen roller shaft.
Each end of both lateral conductive contacts is connected, by any known way from the prior art, to an electrical circuit, in order to transfer the electrical signal from the switch to a device capable to register the signal.
According to an advantageous variant of the present invention at least one of the lateral conductive contacts is designed as pressure means for the conductive shaft so as to urge the platen roller against the thermal printhead. Preferably at least one of the lateral conductive contacts is in the form of conductive spring.
According to another variant of the present invention the printer chassis is conductive and at least one of the lateral conductive contacts is also in contact trough its second end with the printer chassis.
According to yet another variant of the present invention at least one of the lateral conductive contacts is in contact through its second end with a conductive pad located on a flexible circuit. Preferably the flexible circuit is in contact with one of the two lateral conductive contacts through the chassis.
Advantageously the flexible circuit is a single side flexible circuit and is folded on itself in order to generate upper and lower contacts, one of these contacts being electrically connected to the end of the lateral conductive contacts, and the other flexible circuit contact being connected to the chassis.
Advantageously the flexible circuit has two terminals to transfer the signals from the switch to an electronic controller of the printer.
Preferably the flexible circuit first terminal on the area, which is always connected to the printer chassis whatever is the switch position, is connected to the ground on the electronic controller of the printer.
Preferably the lateral conductive contact of the motion means side in the form of a spring is hold by a gear train protector.
According to a preferred variant of the present invention the thermal printhead is firmly mounted onto the printer chassis.
The main advantage of the solution according to the present invention is that using usual pats of the construction provides a reliable sensor for detecting the presence of the platen roller in the thermal printing devices with the so called "easy-loading" system.

BRIEF DESCRIPTION OF THE DRAWINGS

The characteristics of the invention will be disclosed in details in the following description of preferred embodiments, given as non-restrictive examples, with reference to the attached drawings wherein:

Figure 1 is a schematic perspective view of the thermal printing mechanism according to the present invention;
Figure 2 is a schematic perspective view of the inner part of a preferred embodiment of the thermal printing mechanism according to the present invention;
Figure 3 is a schematic detail view of the pressure means and related electrical connections on the motion means side of the thermal printing mechanism;
Figure 4 is a schematic detail view of the motion means side of the chassis of a variant of the thermal printing mechanism showing the mounting of the lateral conductive contact in the form of a spring to the gear train protector;
Figure 5 is a schematic partly exploded detail view of the mounting of the lateral conductive contact in the form of a spring on the side opposite to the motion means;
Figure 6 is a schematic partly exploded detail view of the fixation flexible circuit on the paper guide to ease the protector mounting;
Figure 7 is a schematic detailed view of the upper pad of the flexible circuit and its connection to the printer chassis;
Figure 8 is a schematic detailed view of the lower pad of the flexible circuit and its connection to the spring on the motions side;
Figure 9 is a back view of the mechanism showing the flexible circuit terminals.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS:

Figure 1 schematically shows the thermal printing mechanism according to the present invention. The thermal printing mechanism comprises a printer chassis 2, a thermal printhead 1, a platen roller 3 having a conductive shaft 6, a motion means 11 to put the platen roller 3 in rotation and a paper guide 8. The platen roller 3 is designed to be movable between two possible positions - open position and printing position. The thermal printhead 1 is directly mounted on the conductive printer chassis 2. In alternative variants the thermal printhead can also be assembled in a known way on a rotative support. The motion means 11 for the platen roller is also mounted onto the printer chassis.
As shown on figure 2, the thermal printing mechanism further comprises two lateral conductive contacts 4 and 5 arranged on the printer chassis 2 so as to be in a contact with the two opposite ends of the platen roller conductive shaft 6 in the printing position of the platen roller 3 for conducting electrical current, thus forming an electrical switch for indication of the status of the platen roller position.
Said printer chassis 2 can be conductive or nonconductive.
Said lateral conductive contacts can be made of metallic thin blades, or wire springs, or could be of any know from the prior art type end configuration suitable to realize an electric contact with the two opposite ends of the platen roller conductive shaft 6. The lateral conductive contacts can be mounted directly on the printer chassis 2 or can be mounted to other parts of the mechanism.
In order to transfer the electrical current the lateral conductive contacts are connected to the electrical circuit of the thermal printing mechanism, such connection being realized by any known from the prior art way and means. In the variant of conductive chassis one or both lateral conductive contacts can be connected to the electrical circuit through the chassis.
In a preferred embodiment one or both lateral conductive contacts also implement the function of pressure means for the conductive shaft 6 so as to urge the platen roller 3 against the thermal printhead 1.
Figure 2 shows the inner part of a preferred embodiment of the thermal printing mechanism according to the present invention. The thermal printhead 1 is directly mounted on the conductive printer chassis 2. The platen roller 3 is urged against the thermal printhead 1 by two lateral conductive contacts comprising a wire spring 4 on the motion means side and a wire spring 5 on the opposite side of the chassis. Both wire springs 4 and 5 are in mechanical and electrical contact with the conductive shaft 6 of the platen roller 3 in the printing position. Both first ends 7 of these wire springs 4 and 5 have also a substantially rounded shape in order to manage a hard point when the platen roller 3 engages into the printing position, thus creating a clipsage.
The elasticity of the wire spring 5, urges its second end 20 against the printer chassis 2, thus creating a mechanical and electrical contact between them. Thus the wire spring 5 creates a mechanical and electrical contact between the shaft end of the platen roller on the opposite side of the motion means, and the printer chassis 2.
The partly exploded view on the figure 5 shows one possible variant for the mounting of the spring 5 on a shaft 9 mounted on the paper guide 8.
The wire spring 4 on the opposite side of the print mechanism has a similar substantially round shape if its first end 7 to urge symmetrically the platen roller 3 against the thermal head 1 via the platen roller shaft 6 as shown on figure 2 and figure 3.
Thus the wire spring 4 is in mechanical and electrical contact with the shaft end of the platen roller 3 on the side of the motion means.
The elasticity of the wire spring 4, urges its second end 16 against the flexible circuit 17, thus urging the flexible circuit 17 against the printer chassis 2 as shown on figures 7 and 8.
Said wire spring 4 is mounted on a non-conductive shaft 12 arranged on a gear train protector 10 as shown on the figure 4. This protector 10 is mounted on the paper guide 8 and protects the gear train from dust. It is also used to lock the paper guide 8 in position and has complementary shapes in order to lock all parts of the construction in position. This allows the wire spring 4 to be electrically isolated from the printer chassis 2. The second end 16 of the wire spring 4 is in electrical contact with a flexible circuit 17 in order to electrically close the whole switch circuit.
Preferably two terminals located on the terminal section 18 of the flexible circuit 17 and as shown on figure 9 correspond to both ends of the electrical switch. Said terminals could be used directly to switch on a light like a LED. In a preferred embodiment, both terminals are connected to an electronic controller board which is processing the information coming from the switch, in order to control the printer operation.
Preferably said flexible circuit 17 is a single side flexible circuit, to keep its price low. Two conductive pad areas are made on the flexible circuit 17, in order to generate one upper contact 13 and one lower contact 15, both contacts being one over the other, when the flexible circuit is folded on itself.
Figure 7 shows the upper contact pad 13, and figure 8 shows the lower contact pad 15. When the second end 16 of the wire spring 4, urges the flexible circuit 17 onto the printer chassis 2, the upper contact pad 13 connects to the printer chassis 2, and the lower contact pad 15 contacts the second end 16 of the wire spring 4. Finally, two tracks on the flexible circuit 17 connect these two pads to two corresponding terminals in the terminal section 18 of the flexible circuit 17 as shown on the figure 9.
When the switch is closed, the electricity flows trough the first terminal on the section 18 of the flexible circuit 17, to the printer chassis 2 through the upper contact pad 13, due to the pressure exerted by the second end 16 of the wire spring 4, then to the second end 20 of the wire spring 5, then to the platen roller shaft 6 through the first end 7 of the wire spring 5, and via the first end 7 of the wire spring 4, to the lower contact pad 15 and then to the second terminal on the terminal section 18 of the flexible circuit 17 thanks again to the pressure of the second end 16 of the wire spring 4, thus closing the switch circuitry.
In a preferred embodiment, the first terminal on the terminal section 18 of the flexible circuit 17, which is always connected to the printer chassis 2 via the upper contact pad 13, and thus, whatever is the status of the switch, is connected to the ground on the electronic board. Such connection allows to ground the printer chassis 2 for a better protection against electro-static discharge on the thermal printhead 1. The second terminal is then reflecting the status of the switch, being or not connected to ground according to the status of the switch.
To ease the gear train protector 10 mounting, and avoid that the flexible printing circuit moves or slides during the protector 10 insertion, two pins 19 are arranged on the nonconductive paper guide 8 in order to locate the flexible circuit 17 on the paper guide 8. Then when the paper guide 8 is installed in its final position, as shown for instance on figure 5, the two pins are below the printer chassis 2 and the flexible circuit 17 cannot escape anymore from the two pins 19. Then when the protector 10 is mounted, the second end 16 of the spring 4 can get in mechanical and electrical contact with the flexible circuit 17, which is locked in position, without moving it.
Various modifications and/or additions of parts will be apparent to those skilled in the art that will remain within the field and scope of the present invention defined in appended claims. All the parts may further be replaced with other technically equivalent elements.
Reference signs for technical features are included in the claims for the sole purpose of increasing the intelligibility of the claims and accordingly, such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs.

Claims

Thermal printing mechanism comprising:
- a printer chassis (2),

- a thermal printhead (1),

- a platen roller (3) having a conductive shaft (6), the platen roller (3) being designed to be movable between two possible positions - open, where the platen roller (3) is detached from the printer chassis (2) and printing position where the platen roller (3) is held in the printer chassis (2),

- a motion means (11) to put the platen roller (3) in rotation,
characterized in that
it further comprises two lateral conductive contacts (4 and 5) arranged on the printer chassis (2) so as to be in a contact with the two opposite ends of the platen roller conductive shaft (6) in the printing position of the platen roller (3) for conducting electrical current, thus forming an electrical switch for indication of the status of the platen roller position.
Thermal printing mechanism according to claim 1 wherein at least one of the lateral conductive contacts (4, 5) is designed as pressure means for the conductive shaft (6) so as to urge the platen roller (3) against the thermal printhead (1).
Thermal printing mechanism according to claim 2 wherein said at least one of the lateral conductive contacts (4, 5) is in the form of a conductive spring.
Thermal printing mechanism according to any of the previous claims, wherein the printer chassis (2) is conductive and at least one of the lateral conductive contacts (4 or 5) is also in contact trough its second end (20) with the printer chassis (2).
Thermal printing mechanism according to any of the previous claims, wherein at least one of the lateral conductive contacts (4 or 5) is in contact trough its second end (16) with a conductive pad (15) located on a flexible circuit (17).
Thermal printing mechanism according to claim 5 wherein the flexible circuit (17) is in contact with one of the two lateral conductive contacts (4 or 5) through the chassis (2).
Thermal printing mechanism according to claims 5 or 6, wherein the flexible circuit (17) is a single side flexible circuit and is folded on itself to generate an upper (13) and lower (15) contact pads, one of these contacts being electrically connected to one end of the lateral conductive contact (4 or 5), and the other flexible circuit contact being connected to the chassis (2).
Thermal printing mechanism according to any of claims 5, 6 or 7, wherein the flexible circuit (17) has two terminals to transfer the signals from the switch to an electronic controller of the printer.
Thermal printing mechanism according to any of claims 5, 6, 7 or 8, wherein the flexible circuit (17) first terminal on the terminal section (18), which is always connected to the printer chassis (2), whatever is the switch position, is connected to the ground on the electronic controller of the printer.
Thermal printing mechanism according to any of the previous claims wherein the lateral conductive contact (4) of the motion means (11) side in the form of a wire spring is hold by a gear train protector (10).
Thermal printing mechanism according to any of the previous claims wherein the thermal printhead (1) is firmly mounted onto the printer chassis (2).